During epitaxy on SiC substrate wafers, the heating of the substrate wafer to the deposition temperature is principally effected by contact and heat convection. Since the substrate wafer usually bends during the heating process, the locations at which contact is kept with the heating source are heated to a greater extent than the locations which are no longer in contact with the heating source on account of the curvature. This leads to a non-uniform heating of the substrate wafer. Since the deposition of some materials, in particular semiconductor materials, is extremely temperature-sensitive, temperature inhomogeneities on the growth area lead to large variations in the properties of the deposited semiconductor material. By way of example, a temperature difference of 1° C. during the epitaxy of AlInGaN suffices to cause considerable variations in the emission wavelength of the deposited AlInGaN. Such wide variation of the emission wavelength of the semiconductor material then also impairs the uniformity and therefore the quality of the finished components.
In contrast to this, it is possible to achieve a more uniform temperature on the growth area of the substrate wafer by heating using thermal radiation. In the case of an SiC substrate wafer, however, thermal radiation cannot be used because SiC is transparent in the entire spectral range above about 400 nm and is therefore unable to absorb radiation in this range.
In order to improve the heat input into a substrate wafer during MBE (molecular beam epitaxy), it is known to apply metal layers on the rear side of the substrate wafer, which can absorb the thermal radiation better than the substrate wafer. This method leads to a narrower temperature distribution on the substrate wafer and thus to less variation in the emission wavelength of the deposited, temperature-sensitive semiconductor material.
In MOVPE (metal organic vapour phase epitaxy), such a metal layer has not been used heretofore because an additional layer on the rear side of the substrate wafer possibly leads to contaminants in the reactive gas space. Therefore, at the present time there are no measures known for MOVPE which enable a uniform heating of the substrate wafer in particular of an SiC-based substrate wafer.